Process for producing direct positives by the silver salt diffusion process



United States Patent Ofiice 3,236,642 PRUCESS FOR PRODUCING DIRECTPOSITIVES BY THE SELVER SALT DIFFUSION PRQCESS Harald von Rintelen,Cologne-Rodenkirchen, Siegfried Petersen, Leverkusen, and Max Heilmann,ColognelFlittard, Germany, assignors to Agfa Aktiengesellschaft,Leverkusen, Germany, a corporation of Germany No Drawing. Filed Sept.12, 1961, Ser. No. 137,491 Claims priority, application Germany, Sept.24, 1960, A 35,652 7 Claims. (Cl. 96-29) This invention relates todirect positives as well as to a process for producing the same.

French Patent No. 879,995 describes a process for the direct productionof positives in which the unexposed and, therefore, undevelopable silverhalide of an image-wise exposed photographic silver halide emulsionlayer is dissolved during or after the development of the negative andis transferred in another image-receiving or transfer layer with whichit is in close contact under the catalytic influence of developmentnuclei that are present in this transfer layer which are capable ofprecipitating metallic silver from the dissolved silver salt to form apositive image. The terms negative and positive are in this case usedonly in a relative sense, since it is possible by the same process toobtain directly a negative from a negative original.

This process, which is known as a silver salt diffusion process, is usedinter alia for high-speed copying in business offices, using adeveloping apparatus suitable for this purpose. The present tendency isto arrange for the entire process to be carried out as quickly aspossible, i.e., so that the time of travel through the developingapparatus and thus also the time of contact of the positive with thenegative that is required in such a diffusion process should be as shortas possible.

It has now been found that the production of direct positives by thesilver salt diffusion process can be substantially accelerated andsimultaneously black silver images of high density can be obtained, ifthe process is carried out in the presence of compounds having thegeneral formula in which R represents a hydrogen atom or an aliphaticradical containing from 1 to carbon atoms such as 2 1H-tetrahydropyrimidinethione,

1-methyl-2 1H -tetrahydropyrirnidinethione, l-ethyl-2( 1H-tetrahydropyrimidinethione, 1-propyl-2( 1H)-tetrahydropyrimidinethione,1-n-butyl-2( 1H -tetrahydropyrimidinethione, and 1-n-pentyl-2( 1H-tetrahydropyrimidinethione.

These compounds have also been referred to as2-hexahydropyrimidinethiones.

These 2(1H -tetrahydropyrimidinethiones can be prepared fromN-alkylsubstituted 1,3-propylenediamines and carbon disulfide in amanner analogous to that described by C. F. H. Allen, C. O. Edens andJames Van Allan on pages 34 and 35 of Organic Syntheses, vol. 26,published 1946 by John Wiley & Sons, Inc., New York, for the preparationof ethylene thiourea (Z-imidazolidinethione) from ethylenediamine andcarbon disulfide. 2( lH)-tetrahydropyrimidinethione was described byArthus E. Baum, in United States Patent No. 2,544,746; its preparationfrom 1,3-diaminopropane(1,3-propylenediamine) and car- Patented Feb. 22,1966 bon disulfide was described by A. F. McKay and W. G. Hatton, inJournal of the American Chemical Society, vol. 78, page 1619 (1956).

These 2(1H)-tetrahydropyrimidinethiones are soluble in water and alkaliand are added to the transfer material and/ or to the developer solutionin quantities of between 1 and 200 milligrams per square meter oftransfer material or per liter of developer.

The deposition of the silver is accelerated by the use of thesecompounds, i.e., a black silver image of high density is obtained withcontact times of as little as a few seconds, whereas when using the samematerial without addition of one of these compounds, a longer period ofcontact of the negative with the positive is necessary for obtaining thesame density of the silver image. At the same time, these compoundscause a displacement of the image toning towards bluish-black.

These 2(1H)-tetrahydropyrimidinethiones are moreover characterized bytheir good stability, both in the transfer layers and in the developer.It is especially surprising that they retain their efficacy over a longperiod in positive layers on paper, without migrating into the barytacoating or into the paper raw material, as is frequently the case withother substances, for example, photographic stabilizers.

Various silver halides and their mixtures, such as silver chloride,silver bromide or silver bromoiodide, can be used for the production ofthe light-sensitive negative material, and the said halides or mixturescan if desired'be optically sensitized in the usual manner. All knownlayerforming substances are to be considered as layer formers for thenegative layer, including gelatin, starch, polyvinyl alcohol, cellulosederivatives and the like.

Paper, and films consisting, for example, of cellulose acetate,cellulose nitrate, polycarbonate, polyethylene terephthalate,polystyrene and others are suitable as the base for the silver halideemulsion layer.

A base or support consisting of paper or a plastic film is alsoadvantageously used for the positive material. However, other supportssuch as metal, textile fabric and the like can also be used. For theproduction of such a positive material, a layer which containsdevelopment nuclei, such as colloidal noble metals or metal sulfides,and, if necessary, a silver halide solvent may be applied to such asupport. As layer former for the positive layer, a hydrophilic colloidis advantageously used, such as gelatin, casein, carboxymethylcellulose, starch, starch ethers, starch esters, galactomannanspolymannuronic acids, polymannuronic acid esters, polymannuronic acidamides, polyvinyl alcohol and its derivatives or the like.

All prior known developer substances which have been used for thedevelopment of films and papers can be used in the development processof the present invention. The developer solution can contain a silverhalide solvent as well as conventional developer additives, such aspreservatives, wetting agents and the like. The developer substance canalso be added to the negative layer and/or to the positive layer.

The process is more fully described in the following examples:

Example 1 A support, for example, a sheet of paper, has applied theretoa solution of the following composition:

Gelatin g 70 Ag S (colloidal) g 0.03 Formaldehyde solution (30 percent)ml 10 Water to make 1 liter.

which also contains 0.025 grams per liter of l-methyl-2(1H)-tetrahydropyrimidinethione (M.P.== 123 C.)

A gelatino-silver chloride layer exposed through an original by reflexcopying is developed in a developer having the following composition andbrought into contact with the positive:

G. Anhydrous sodium sulphite 70 Hydroquinone 16 l-phenyl-3-pyrazolidone1 Potassium bromide 1.5 Sodium hydroxide Sodium thiosulphate Water tomake 1 liter.

After a contact time of 10 seconds, a dense black silver image of theoriginal is obtained.

Example 2 A sheet of paper is coated as in Example 1 with a layer whichcontains a white pigment, for example, barium sulfate. To the said layeris then applied a layer having the following composition:

G. Carboxymethylcellulose of low viscosity 40 Sodium thiosulphate1-ethyl-2( 1H)-tetrahydropyrimidinethione 0.032 Water to make 1 liter.

After development in a developer having the composition:

G. Anhydrous sodium sulphite 7O Hydroquinone 16 1-phenyl-3-pyrazolidone1 Potassium bromide 1.5 Sodium hydroxide 10 Water to make 1 liter.

and after the transfer, results equally as good as those of Example 1are obtained.

Water to make 1 liter.

an exposed negative is developed in contact with a transfer material,which is obtained by application of the following solution to a sheet ofpaper:

Gelatin 80 Carboxymethyl cellulose 20 Ag S (colloidal) 0.03 Sodiumthiosulphate Water to make 1 liter.

Using this material, positive images of better density and deeper blacksare obtained than with the same material and developer without additionof 1-methyl-2(1H)-tetrahydropyrimidinethione.

Example 4 To a sheet of paper is applied a solution having the followingcomposition:

Gelatin 150 Carboxymethyl cellulose 22' Ag S (colloidal) 0.05 Sodiumthiosulphate 60 2(1H)-tetrahydropyrimidinethione 0.03

Water to make 1 liter.

This positive material and an exposed negative are each moistened in adeveloper as in Example 2 and thereafter brought into contact with eachother. After a contact time of about 12 seconds, a deep black positiveimage of the original is obtained.

The foregoing examples illustrate methods of using2(1H)-tetrahydropyrimidinethiones in accordance with the processes andproducts of the present invention. It is to be understood, however, thatthese examples are preferred embodiments, and are not to be consideredas limiting the invention thereto. It is clear to those skilled in theart that the practice of the invention lends itself readily to a numberof useful modifications, especially with regard to the ingredients ofthe light-sensitive photographic material, the transfer material and thedeveloper composition, for example, as developers, numerous conventionalproducts are useful, e.g., p-methyl aminophenol, p-aminophenol,hydroquinone, diaminophenols, 4-aminopyrazolones andl-aminophenyl-3-aminopyrazolones, and the developer composition may bealkalized by adding thereto alkali-metal hydroxides, alkali-metalcarbonates or tertiary alkali-metal phosphates. The developers maycontain any stabilizing agents, anti-fog agents and antioxidants, suchas alkali-metal sulphites or salts of hydroxylamine. Chemical compoundswhich can be used as silver halide solvents include, for example,water-soluble thiosulphates, such as alkali-metal thiosulphate, ammoniumthiosulphate and alkaline earth thiosulphates.

What is claimed is:

1. In a process for the production of a direct positive print from anoriginal by developing an imagewise-exposed light-sensitive silverhalide emulsion layer in a silver halide developer solution containing asilver halide solvent and contacting the silver halide emulsion layerduring the course of the development with an image-receiving layer thatis insensitive to light and contains development nuclei, in whichdeveloping process the silver halide from the unexposed areas of thesilver halide emulsion layer is dissolved and transferred to the saidimagereceiving layer and is reduced on the said image-receiving layer toa silver image, the improvement of contacting the silver halide emulsionlayer with the image-receiving layer in the presence of a2(1H)-tetrahydropyrimidinethione having the general formula wherein Rstands for a radical selected from the group consisting of hydrogen andalkyl radicals containing from 1 to 5 carbon atoms.

2. A process as defined in claim 1 in which the 2(1H)-tetrahydropyrimidinethione is added to the developer.

3. A process as defined in claim 1 in Which the 2(1H)-tetrahydropyrimidinethione is added to the image-receiving layer.

4. A process as defined in claim 1 in which the 2(1H)-tetrahydropyrimidinethione is added to both the imagereceiving layer andthe developer solution.

5. An image-receiving material that is insensitive to light whichcomprises a paper support coated with a layer of a hydrophilic colloidalsubstance containing development nuclei and containing an amount betweenabout 1 and 200 milligrams per square meter of surface of a2(1H)-tetrahydropyrimidinethione having the general formula wherein Rstands for a radical selected from the group r 5 6 consisting ofhydrogen and alkyl radicals containing 1 to in which R is a radical ofthe group consisting of hydro- 5 carbon atoms. gen and alkyl radicalscontaining from 1 to 5 carbon 6. The image-receiving material accordingto claim 5 atoms. wherein the hydrophilic colloidal substance isselected from the group consisting of gelatin, casein, carboxy 5References Cited y the Examine! methyl cellulose, starch, starch ethers,starch esters, galac- UNITED STATES PATENTS tomannans, polymannuronicacids, polymannuronic acid esters, polymannuronic acid amides, polyvinylalcohol 2901351 8/1959 Van ee et a1 260 256'5 and polyvinyl alcoholderivatives. 3017270 1/1962 Tregluus 9629 7. An aqueous alkalinedeveloper solution containing a developer for silver halides and between1 and 200 10 FOREIGN TE milligrams per liter of a2(1H)-tetrahydropyrimidine- 753, 7/ 1956 Great Brltaln- 783,793 10/1957Great Britain.

thione having the general formula 867,174 5/1961 Great Britain.

H: 15 OTHER REFERENCES 1 Chemical Abstracts, 46, 3885 1952 HzC C=SNORMAN G. TORCHIN, Primary Examiner.

1. IN A PROCESS FOR THE PRODUCTION OF A DIRECT POSITIVE PRINT FROM ANORIGINAL BY DEVELOPING AN IMAGEWISE-EXPOSED LIGHT-SENSITIVE SILVERHALIDE EMUSLION LAYER IN A SILVER HALIDE DEVELOPER SOLUTION CONTAINING ASILVER HALIDE SOLVENT AND CONTACTING THE SILVER HALIDE EMULSION LAYERDURING THE COURSE OF THE DEVELOPMENT WITH AN IMAGE-RECEIVING LAYER THATIS INSENSITIVE TO LIGHT AND CONTAINS DEVELOPMENT NUCLEI, IN WHICHDEVELOPING PROCESS THE SILVER HALIDE FROM THE UNEXPOSED AREAS OF THESILVER HALIDE EMULSION LAYER IS DISSOLVED AND TRANSFERRED TO THE SAIDIMAGERECEIVING LAYER AND IS REDUCED ON THE SAID IMAGE-RECEIVING LAYER TOA SILVER IMAGE, THE IMPROVEMENT OF CONTACTING THE SILVER HALIDE EMULSIONLAYER WITH THE IMAGE-RECEIVING LAYER IN THE PRESENCE OF A2(1H)-TETRAHYDROPYRIMIDINETHIONE HAVING THE GENERAL FORMULA
 7. ANAQUEOUS ALKALINE DEVELOPER SOLUTION CONTAINING A DEVELOPER FOR SILVERHALIDES AND BETWEEN 1 AND 200 MILLIGRAMS PER LITER OF A2(1H)-TETRAHYDROPYRIMIDINETHIONE HAVING THE GENERAL FORMULA